1. Field of the Invention
The present invention relates to a method of manufacturing a pipe.
2. Description of the Related Art
It is a conventional practice, in an automobile exhaust pipe or the like, to provide a partition plate in the pipe to make a plurality of parallel flow channels.
For the manufacture of such a pipe, there have conventionally been available a method of forcing a long plate-shaped partition plate into a cylinder, and a method of dividing a sheet type base plate into three in the width direction, and folding the base plate at both sides in opposite directions into an S-shaped cross-section so that the center portion of the base plate forms a partition plate, thereby providing a plurality of parallel flow channels, as disclosed, for example, in JP-U-63-196425, JP-A-04-6397 and JP-A-04-294835.
In the former manufacturing method, it is difficult to force a long partition plate into a long cylinder.
In the latter manufacturing method, a side of the base plate is first folded, and then the other side is folded, i.e., in different steps, both sides are folded, respectively. It is therefore necessary to use special die jigs such as exclusive inner dies and exclusive outer dies for folding the respective sides in the different steps, thus resulting in a longer manufacturing time and a higher manufacturing cost. In addition, necessity of replacing jigs and dies during an interval between the two folding steps may lead to occurrence of a working error, thus making it difficult to obtain an accurate sectional shape. This results in an unstable shape of the bent portion (weld joint) of the partition plate with which the leading end of the folded side comes into butt contact, thus leading to a decrease in welding quality.
The present invention has therefore an object to provide a method of manufacturing a pipe, which permits resolution of these problems.